DEVELOPMENT OE THE TONGUE 



151 



in the mid-ventral line from the bases of the third and fourth branchial arches. 

 This is the anlage of the epiglottis. In later stages (Fig. 156 A and B) the lateral 

 mandibular anlages, bounded laterally by the alveolo-lingual grooves, increase 

 rapidly in size and fuse with the tuberculum impar, which lags behind in develop- 

 ment and is said to form the median septum of the tongue. According to Ham- 

 mar, it atrophies completely. The epiglottis becomes larger and concave on its 

 ventral surface. Caudal to it, and in early stages continuous with it, are two thick 

 rounded folds, the arytenoid ridges. Between these is the sht-hke glottis leading 

 into the larynx (see p. 165). 



Lateral tongue swellings Thyreoid diverticulum 



Lateral tongue swellings 



III I a nee to 

 larynx 



trance to 

 arynx 

 vtenoid 

 ilings 



Fig. 157. — The development of the tongue in human embryos. A, 5 mm.; B, 7 mm. (modified from 



Peters). 



The foregoing account applies to the early origin of the mucous membrane alone. The 

 musculature of the tongue is supplied chiefly by the hypoglossal nerne, and both nerve and 

 muscles develop caudal to the branchial region in which the tongue develops. The muscu- 

 lature migrates cephalad and gradually invades the branchial region beneath the mucous 

 membrane. At the same time, the tongue may be said to extend caudad until its root is cov- 

 ered by the epithelium of the third and fourth branchial arches. This is shown by the fact 

 that the sensory portions of the nn. trigeminus SLud facialis, the nerves of the first and second 

 arches, supply the body of the tongue, while the nn. glossopharyngeus and vagus, the nerves of 

 the third and fourth arches, supply the root and the caudal portion of the body of the tongue. 



In fetuses of 50 to 60 mm. (C R) the fungiform axiA filiform papillae may be dis- 

 tinguished as elevations of the epitheHum. Taste buds appear in the fungiform 

 papillae of 100 mm. (C R) fetuses and are much more numerous in the fetus than 

 in the adult. The vallate papillce (Fig. 158 A) appear as a V-shaped epithelial 

 ridge, the apex of the V corresponding to the site of the thyreoid vagination 

 (foramen cacum). At intervals along the epithehal ridges circular epithehal 

 downgrowths develop (85 mm. C R) which take the form of inverted and hollow 

 truncated cones (Fig. 158). During the fourth month circular clefts appear in 

 the epithelial downgrowths, thus separating the walls of the vallate papillae from 



